The production of metal-ceramic substrates and especially copper-ceramic substrates for electrical wiring and circuits is known in the most varied versions. Producing the metal coating which is required for producing conductive tracks, terminals, etc. on a ceramic, for example on an aluminum oxide ceramic, using so-called “DCB process” (direct copper bond technology) is also especially known here, using metal or copper foils, or metal or copper sheets which form the metal coating and which on their surface sides have a layer or a coating (melted-on layer) of a chemical compound of a metal and a reactive gas, preferably oxygen. In this process, which is described for example in U.S. Pat. No. 3,744,120, or DE-PS 23 19 854, this layer or this coating (melted-on layer) forms a eutectic with a melting point below the melting point of the metal (for example, copper) so that by placing the foil on the ceramic, and by heating all the layers, they can be joined to one another by melting on the metal, or copper, essentially only in the area of the melted-on layer or oxide layer. This DCB process then has the following process steps:
oxidization of a copper foil such that a uniform copper oxide layer results;
placing the copper foil on the ceramic layer;
heating the composite to a process temperature between roughly 1025 to 1083° C., for example to roughly 1071° C.; and
cooling to room temperature.
After applying the metal foils, at least on the surface side of the ceramic layer, structuring of the metal foil there, for example copper foil (also DCB copper), takes place to form conductive tracks, contact surfaces, etc.
Furthermore, the so-called active brazing process (DE 22 13 115; EP-A-153 618) is known, especially for producing metal-ceramic substrates. In this process, at a temperature between roughly 800-1000° C., a bond is formed between a metal foil, for example, copper foil, and a ceramic substrate, for example aluminum nitride ceramic, using a brazing solder which in addition to the main components such as copper, silver and/or gold, also contains an active metal. This active metal, which is for example one element of the group Hf, Ti, Zr, Nb, Cr, produces a bond between the brazing solder and the ceramic by a chemical reaction, while the bond between the brazing solder and the metal is a metallic brazing bond.
The production of metal-ceramic substrates takes place in a multiple printed panel such that on a ceramic substrate with a large area several individual substrates are formed spaced apart from one another and each have conductive tracks, contact surfaces, etc. On scored lines, which are made in the ceramic substrate by means of a laser, this multiple printed panel can be divided later into individual substrates by breaking, for example, after assembly.
An object of the invention is to devise a process with which the production of metal-ceramic substrates with improved properties is easily possible.